1. Field of the Invention
The invention relates to a bidirectional valve and a fuel shut-off device. In particular, the invention relates to a bidirectional valve for passing gasoline vapor in two directions and a fuel shut-off device placed in a fuel tank for passing gasoline vapor between the fuel tank and an external device such as a canister in both directions while at the same time preventing outflow of liquid fuel to the external device.
2. Description of Related Art
Hitherto, a bidirectional valve like the valve disclosed in Japanese Patent Laid-Open No. 60-184,779 has been disposed between the fuel tank and the canister. The bidirectional valve helps protect the fuel tank as the vapor pressure therein rises or falls. A conventional bidirectional valve will be described with reference to FIG. 5. The conventional bidirectional valve 200 has: (1) a partition 206 that divides the inside of a case body 202 into an upper valve chamber 203 and a lower valve chamber 204, (2) a check valve 210 provided in the upper valve chamber 203 which is sealed by a cover member 212, and (3) a diaphragm valve 220 provided in the lower valve chamber 204 which is sealed by a cover member 222.
In this conventional construction, a rise in the internal pressure of the fuel tank to above atmospheric pressure and in excess of a predetermined amount causes an increase in pressure at tank port TP adjacent to the tank. Hence, the pressure on the diaphragm valve 220 of lower valve chamber 204 increases through a path (path not shown). In turn, this causes the valve body 224 to oppose spring 226 and open away from a valve seat surface 228, allowing fuel vapor to escape from the fuel tank to the canister.
On the other hand, when the internal pressure of the fuel tank has dropped so that the pressure difference between the tank port TP and the canister port CP becomes greater than a predetermined value, the valve body 214 of the check valve 210 opposes the spring 216 through a spring receiving member 217 and opens away from a valve seat surface 218. This allows fuel vapor to return from the canister to the fuel tank.
In general, a conventional bidirectional valve 200 having the above-described construction and function is used together with a fuel shut-off device. The fuel shut-off device prevents outflow of liquid fuel from the fuel tank while at the same time allowing fuel vapor to be discharged from the fuel tank to external devices such as canisters (refer to Japanese Patent Laid-Open No. 4-228,321). In this case, the tank port TP of the bidirectional valve 200 must be connected to a fuel vapor discharging path of a fuel shut-off device by means of an oil proof hose.
In the aforementioned conventional bidirectional valve 200, the check valve 210 is assembled through an opening in the upper valve chamber 203, while the diaphragm valve 220 is assembled through an opening in the lower valve chamber 204. Therefore, it is necessary to assemble the check valve 210 and the diaphragm valve 220 from different directions. Assembly becomes complicated because the diaphragm valve 220 can be assembled only after the check valve 210 is completed and the valve body 214 has been turned over.
In the bidirectional valve 200, the openings of the upper valve chamber 203 and the lower valve chamber 204 must be sealed air-tightly. Therefore, it is necessary to seal carefully the openings of the upper valve chamber 203 and the lower valve chamber 204 with cover members. This is very troublesome.
However, a fuel shut-off device that could be combined together with the bidirectional valve 200 would be advantageous. Integration of the tank port TP of bidirectional valve 200 and the fuel vapor discharging path of the fuel shut-off device means that a connecting hose does not have to be used. However, if the fuel shut-off device and the bidirectional valve 200 are formed into a combined structure with the bidirectional valve 200, the fuel shut-off device must also be turned over, making assembly of such a structure difficult.